This invention relates to a method of depositing dry powders on a substrate, and in particular, medicaments for use with inhalers, for example, and inhaler devices for use with such substrates.
Dry powder inhalers are used as drug delivery devices for pharmaceutical compounds to individuals. In these devices, a pharmaceutical powder is deposited on a surface of a substrate. The substrate may then be supplied in the inhaler as a cassette, a cartridge and so on. When the patient requires medication, the ideal dry powder inhaler forms a fine particle cloud that is to be inhaled and thereby delivers a high respirable fraction of the stored dose deeply into the patients lungs. In most cases, the deep recesses of the lung is the desired site for the drugs in the inhaled powder cloud.
This can be most efficiently achieved by:
1. Releasing a high fraction of the deposited drug and
2. Insuring that the powder cloud consists of individual particles or particle aggregates between 1 xcexcm and 5 xcexcm.
As individual particles are reduced below 10 xcexcm, both release and particle aggregation become serious hindrance to delivering a high respirable fraction deeply into the patient""s lungs.
A common problem dealt with by various prior art inhaler apparatuses for dispensing dry powder medicaments is providing for a controlled reliable release of the medicament. The dry powder inhalers may be loaded with medicaments by filling techniques not involving electrostatics. In certain implementations, the deposited powder tends to form agglomerated particles resulting in uncontrolled variation in the amount of medicament released. Several of the aforementioned applications provide various solutions to this problem.
Numerous approaches have been taken in the design of dry powder inhalers. In some cases, the powder is released by impact of a substrate powder carrier, as disclosed in WO 93/09832. Of interest is an inhaler as disclosed in WO 90/13328.
In copending applications Ser. Nos. 661,213 and 661,212, indentations or raised surfaces are disclosed in the inhaler interior surfaces having contact with the medicament for inhalation, the surfaces minimizing the area of contact between the medicament and the surfaces of the inhaler apparatus, promoting the release of the medicament from the inhaler.
Where particles of medicament agglomerate, they impact the mouth and throat rather than remain in the air flow for deposition in the lungs. One remedy is to provide tortuous channels in the inhalers to promote deagglomeration. However, the medicament may be deposited along the channels leading to inaccurate dosage dispensing. Agglomeration also results in the inhaler tending to dispense the medicament inaccurately so that greater or lesser amounts are dispensed. The aforementioned solutions to the problem of agglomeration tend to rely on mechanical devices for minimizing agglomeration effects.
The small particle size required for transport to the lung presents a number of problems for release by the inhaler and delivery to deep lung regions. As the particle size decreases, the relative bonding force between the particle and other objects increases. This applies to both particle-to-substrate bonding and particle-to-particle bonding. As a result, particle aggregates become more tightly bound and individual particles are more difficult to remove from the substrate. Aggregation increases the effective size of the drug released and diminishes the respirable fraction. The increase in relative particle-to-substrate bonding makes drug release more difficult and also decreases the respirable fraction.
The present inventors recognize a need for a different approach wherein the agglomeration itself is minimized so as to be negligible. This reduces the need for mechanical solutions to deal with the agglomeration effects.
A method of depositing a dry powder on a substrate according to the present invention comprises providing a plurality of elongated dry particles each having a longitudinal axis and depositing the particles on a surface of a substrate with the longitudinal axes aligned substantially normal to the substrate surface.
Preferably the method includes in one embodiment charging the particles with a given polarity and electrostatically depositing the particles on the substrate.
In a further embodiment, the particles are provided with an aspect ratio such that an electrical dipole is created in the particles along the axis. An electrical field attracts the particles to the substrate.
In a still further preferred embodiment, the particles have an aspect ratio of about 2:1.
The substrate may be metallic, or non-metallic including mesh and non-mesh materials.
In a further embodiment, a controlled amount of the medicament is deposited at each of a plurality of predetermined regions on the surface of the substrate.
The particles in a further preferred embodiment have a diametrical dimension in the range of about 0.5 xcexcm to 3 xcexcm and a length in the range of about 1 xcexcm to 10 xcexcm.
In a further embodiment, the particles are a pharmaceutically active ingredient medicament.
A device for dispensing a pharmaceutical drug according to a further embodiment of the present invention comprises an inhaler having a mouthpiece and a medicament cavity in communication with the mouthpiece. A dry powder medicament deposited in discrete spaced locations on a substrate is introduced into the cavity for selective dispensing by the inhaler, the medicament comprising a plurality of elongated particles, the particles having an aspect ratio such as to create an electrical dipole in the particles when charged or induced by the depositing field.
A device according to a still further embodiment of the present invention for depositing a dry powder on a substrate comprises a plurality of elongated dry particles each having a longitudinal axis and means for depositing the particles on a surface of a substrate with the longitudinal axes aligned substantially normal to the substrate surface.